FIG. 1 is an exploded perspective view showing a conventional centrifugal clutch power transmission mechanism, which is disclosed in Korean Utility Model Registration No. 0237307 (entitled “electrical screw driving tool”), and an operation principle of the conventional centrifugal clutch power transmission mechanism will be described below.
If a motor does not operate or rotates at a low speed, a lever 17 is pushed to the right side in the drawing through the operation of a spring 8, and an elevating rod 16 connected with the lever 17 through a cam 18 is moved down and escaped from a concave groove 23 of a wing 20. In this state, a spindle 7 is coupled freely rotatable to an inertia wheel 5, and therefore, even though the inertia wheel 5 rotates, the spindle 7 does not rotate. If the rotational speed of the motor reaches a given speed or more, the centrifugal force applied to a starter 10 mounted on the inertia wheel 5 exceeds the elastic force of the spring 8, and accordingly, the starter 10 is moved outward to pull the lever 17, so that the elevating rod 16 is moved up by the operation of the cam 18 and engaged with the concave groove of the wing 20 on the top end periphery thereof, thus hitting and rotating the spindle 7. If substantially large resistance occurs during the rotation to cause the rotational speed of the motor to be decreased, the centrifugal force applied to the starter 10 is not sufficient to allow the starter 10 and the lever 17 to be returned to their original position by the operation of the spring 8, and thus, the elevating rod 16 is moved down by the operation of the cam 18 and escaped from the concave groove 23, thus stopping the rotation of the spindle 7. If the rotational speed of the motor reaches the regulation speed again, the above-mentioned process is carried out again to generate torques needed for mounting/demounting bolts or nuts.
The conventional power transmitting mechanism using the centrifugal force does not immediately transmit the rotational force of the motor to the spindle 7 during the initial operation due to the gaps among the starter 10, the lever 17, the cam 18, and the elevating rod 16, and the elevating rod 16 collides against the concave grove 23 of the wing 20 during the upward movement and thus moved down. After that, the elevating rod 16 is moved up again by the operations of the starter 10, the lever 17, and the cam 18. The downward and upward movements are repeatedly carried out (which is called “chattering”), thus decreasing the transmission efficiency of the rotational force.
Furthermore, the starter 10, the lever 17, the cam 18, and the elevating rod 16 are connected to one another through complicated articulated structures, thus increasing the manufacturing cost and decreasing the durability of the product.
Moreover, separate shock absorbing means is not suggested so that the shock and vibration generated during the working are totally transmitted to a user.